In stock car racing, a race car will typically race on an oval track measuring approximately ¼ mile to 2.66 miles in length. Oval tracks are classified as short track (less than 1 mile), intermediate or speedway (1 to 2 miles), or superspeedway (over 2 miles) and have 3 or 4 turns—all to the left. Top level races are 200 to 600 miles long, during which a race car may reach speeds in excess of 200 mph.
The National Association for Stock Car Auto Racing (NASCAR) is the largest sanctioning body of stock car racing in the United States and sanctions the races of the Sprint Cup Series, the Nationwide Series, and the Camping World Truck Series, to name a few. Of the various technical requirements imposed by NASCAR on the race cars or race trucks (collectively referred to as “race cars”), all race cars in the top three series must use racing tires manufactured by Goodyear Tire and Rubber Company. Due to the performance and safety requirements, racing tires are technological marvels compared to the more ubiquitous passenger tires or even so-called high performance, though less-common, street-racing tires. Racing tires for use in NASCAR sanctioned races must maintain structural integrity at high rotation rates and under adverse loading conditions, such as in high-speed left turns. Such loading conditions are generally not experienced by passenger tires or even by high performance street tires.
The driving conditions experienced by tires used on race cars are significantly different from day-to-day driving experienced by passenger-car tires. For one, the race cars are significantly different from passenger cars. While race cars for racing in NASCAR sanctioned races are roughly equivalent in weight to a passenger car, race cars may reach speeds in excess of 200 mph due to their 900+ horsepower engines. By comparison, most passenger car engines have less than one-half of the horsepower, at most, and do not ordinarily accelerate at the rate that a race car does or reach speeds of even 100 mph over any prolonged period.
Furthermore, the race track is different from a day-to-day road on which a passenger car rides. The loading on the tire due to the shape of the race track is a repetitive, asymmetrical-type loading. For example, most of the Sprint Cup races are on oval tracks, where the race cars travel in a counter-clockwise direction such that the turns are all to the left. Passenger car tires, on the other hand, experience a more equal, all-around loading owing to the nearly equivalent number of left and right hand turns.
Another difference between day-to-day driving and organized racing is the condition of the road surface. For safety, NASCAR races are only held on dry, paved tracks. By comparison, normal road surfaces may be gravel, dirt, asphalt, or concrete and may be dry, wet, snowy, or icy or a combination of these conditions. Thus passenger tires must have good handling characteristics when operated in a variety of road surface conditions, not just under ideal road conditions. Because of the disparity in required performance under the above-mentioned conditions, technology used in passenger or similar tires is generally not transferable to racing tires.
Of the conditions experienced by racing tires, particularly those developed for use in NASCAR sanctioned racing, the continuous left-hand turns in combination with other factors (e.g., high speeds) are possibly the most detrimental condition to the tire's performance. While the turns are banked from 6 to 36 degrees, the repetitive directional loading on the tires causes them to wear unevenly. The type and severity of the uneven wear varies by position on the race car. For instance, the right front tire is the most highly loaded while the remaining tires are loaded to a lesser degree than the right front tire. Accordingly, the performance requirements for each tire position on the car are dissimilar. While various strategies have been proposed and used to counter this problem, none of these strategies have been fully effective.
Therefore, there is a need for an improved tire that can endure the racing conditions on a paved, oval race track, while having good traction and wear resistance and while maximizing the relatively short usable life of the race tire.